1. Field of the Invention
The present invention relates to a toner recycle technique in a case where an image forming processing using toners of plural colors is performed.
2. Description of the Related Art
Heretofore, there is known an image forming apparatus adopting a so-called cleaner-less process in which after a toner image formed on a photoconductive body is transferred onto a transfer member, a toner remaining on the photoconductive body is collected in a developing unit and is reused (see JP-A-5-341643, JP-A-11-249452, Japanese Patent No. 2675554, JP-A-2002-132002, U.S. Pat. No. 4,727,395, JP-B-6-77166, Japanese Patent No. 2879883).
However, in the image forming apparatus adopting the cleaner-less process, although a cleaner-less structure is realized for the photoconductive body, waste toner is produced on an intermediate transfer body, and it can not be said that there is no waste toner in the whole apparatus. In the related art, the waste toner produced on the intermediate transfer body is discarded, and there has been a problem from the viewpoint of toner consumption cost and maintenance cost.
Then, there is disclosed a structure in which a cleaner is provided for an intermediate transfer body, and a toner removed there is returned to a black developing unit (see JP-A-2002-189335, JP-A-2002-311669, JP-A-2001-154439). In the image forming apparatus of the structure, a large amount of secondary transfer residual toner produced in the case where the intermediate transfer body is adopted can be effectively reused, however, the recycle mechanism becomes complicated. Besides, when the cleaner exists for the belt, it is difficult to control the meandering of the belt, and there is also a problem that a complicated mechanism is required. Besides, the belt is scraped by the cleaner, and the life of the belt becomes short, and further, since the cleaner itself has a life, the exchanging operation thereof and the like are required.
In the technique of the structure in which the toner removed from the intermediate transfer body is returned to the black developing unit, there is also disclosed an example in which the transfer residual toner is returned to the photoconductive body by a bias, and is finally collected in the black developing unit. However, when the whole is returned to the black developing unit by such a method, the amount of mixing of different color into the black developing unit is increased, and in some cases, the black color is also changed, and this is not preferable.
Besides, there is disclosed a technique in which respective color toners are individually collected, and when the amount of collection becomes a specific amount, they are mixed and reused (see JP-A-2003-140428, JP-A-2003-345096), in this case, the mechanisms of a collecting device, a transporting device, a mixing device and the like become complicated. Further, any of these are not the cleaner-less process.